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Added in SQL Server version:

Pre-2005/2005

Removed in SQL Server version:

N/A

Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 272 in 2008 and 2008 R2, 279 in 2012, and 286 in 2014 RTM. After 2014 RTM, you must check the DMV to get the latest value as some map_key values have changed in later builds.

Other information:

I have not seen this wait type be a noticeable contention point.

Known occurrences in SQL Server(list number matches call stack list):

Waiting for access to the processor affinity settings (in this case, when creating a task to handle Service Broker messages as part of database mirroring)